Devices and methods of the abovementioned type are used in cryptographic methods, for example, in order to form signatures from input signals specifiable by a user. Modern cryptographic methods, according to AES, advanced encryption standard, for example, are usually protected sufficiently well against “brute force” attacks, based on comparatively great key lengths and the complexity of the method at the current state of computing technology. That is why attacks on cryptographic methods are directed, at this time, increasingly on specific implementations, which are usually implemented by certain electronic circuits. Within the scope of so-called side channel attacks, for example, an attacker tries to obtain information via the current usage of a device implementing the cryptographic method which permit drawing a conclusion on the algorithm or a secret key used by the device. Similar inferences are also possible from electromagnetic fields radiated by the device.
In one attack method also designated as differential power analysis (DPA), operand-dependent current characteristics of a subfunction of the cryptographic method is ascertained in response to as many as possible different input data, and while using a model of the attacked cryptographic algorithm, the method having different keys is submitted to a correlation analysis.